Rainfall intensity duration frequencies, Runoff, Watersheds
The objectives of this research were to derive a design 24-hour duration rainfall distribution for use in southwest Florida, and peak rate factors for use in the Soil Conservation Service (SCS) unit hydrograph method for two watersheds, also in the southwest Florida area. The rainfall distribution is derived by applying a least squares polynomial curve fitting technique to National Weather Service hourly rainfall data collected in the study area. The screening criteria for data included in the curve fitting procedure are: storm duration of 18 to 26 hours, at least three inches of rainfall volume, and peak intensity period falling near the center of the storm. The analysis technique includes converting the raw data to dimensionless form which allows the flexibility of applying the 24-hour storm. Peak rate or attenuation factors are determined for the Hickory Creak (2400 acres) and the Gallagher Ditch (300 acres) the U.S. Geological Survey is used for the analysis. The screening criteria for the hydrographs produced from this data include a stable baseflow condition and a single hydrograph peak. The resulting hydrographs provide input to the Soil Conservation Service triangular unit hydrograph. An average of the peak rate factors calculated from the screened hydrographs is taken as the suitable factor for each watershed. The project results are then compared to the currently used rainfall distributions and the SCS peak rate default value of 484. The comparisons are accomplished by modeling a hypothetical watershed using both the SCS unit hydrograph and the Santa Barbara methods. The model Is run on a microcomputer using seven distributions, three return frequency volumes of rainfall, differing watershed sizes, times of concentrations and antecedent moisture conditions. The conclusion recommends a rainfall distribution and peak rate factor best suited to estimate hydrographs.
Wanielista, Martin P.
Master of Science (M.S.)
College of Engineering
Civil Engineering and Environmental Sciences
Length of Campus-only Access
Masters Thesis (Open Access)
Dendy, Geoffrey S., "24-Hour Rainfall Distribution and Peak Rate Factors for Use in Southwest Florida" (1987). Retrospective Theses and Dissertations. 5038.